1. Field of the Invention
The present invention relate to a spin transistor, and more particularly, to a spin transistor useful for device miniaturization and high-density integration.
2. Description of the Related Art
In an integrated circuit (IC) technology, a metal oxide semiconductor field effect Transistor (MOSFET) has been widely used as a basic component for various electronic devices. For example, a memory device such as a dynamic random access memory (DRAM) and a flash memory, an application specific integrated circuit (ASIC) device, a microprocessor, a logic circuit, and the like have been operated by on/off operations of the MOSFET. Recently, as a substitute for the MOSFET, a spin transistor has been actively researched. In a conventional FET device based on a semiconductor, charges in the semiconductor are controlled by using an electric field. In the spin transistor, spins as well as charges are controlled. Namely, a switching device or a logic device is implemented by controlling spin-polarized charges.
In the MOSFET used as a basic component in the current semiconductor devices, a voltage of the MOSFET is written and read by charging and discharging of charges, so that power consumption and area are difficult to reduce. In addition, there is a physical limitation to a gate oxide layer. As one of next-generation devices for solving the problems of the MOSFET, transistors of controlling a voltage thereof by using precession of electron spins have been proposed. Among such transistors using electron spins, a spin transistor includes ferromagnetic source and drain, and a semiconductor channel interposed between the source and drain.
In a Datta-Das type spin transistor (published in Applied physics letter, vol 56, 665, 1990) and a similar spin transistor (disclosed in U.S. Pat. No. 5,654,566, titled, “Magnetic Spin Injected Field Effect Transistor and Method of Operation”), spin injection from a ferromagnetic source to a semiconductor channel or from the semiconductor channel to a ferromagnetic drain needs to be performed. Due to the spin injection, the ferromagnetic source and drain having shape anisotropy are magnetized in a channel direction so that an electron spin direction is defined. Therefore, the ferromagnetic source and drain are designed to be elongated in the channel direction. As a result, a size of the spin transistor is also increased in the channel direction.